The present invention relates a recording apparatus in which a light beam is applied to a recording medium to form pits or grooves therein.
A conventional recording apparatus of this type is constructed as shown in FIG. 1. In this apparatus, a light beam 1 is modulated by an optical modulator 2 and its diameter is increased to a desired value by a beam expander 3. The light beam thus treated is applied through a beam splitter 4 to a mirror 5. The light beam reflected from the mirror 5 is focused on a recording medium 7 by a focusing lens 6. The light beam reflected from the recording medium 7 is returned through the lens 6, the mirror 5 and the beam splitter 4 to a focus servo system 8. The focus servo system 8 detects the light beam 9 thus returned to control the position of the lens 6 with respect to the recording medium 7 so that the focusing condition of the lens 6 is maintained accurate and stable.
In recording pits with the above-described conventional recording apparatus, the pits can be changed in configuration (length, width and depth) by controlling the irradiation time and the recording power of the light beam 1 with the optical modulator 2. In recording grooves with the apparatus, the grooves can be changed in configuration (width and depth) by controlling the recording power of the light beam 1. For instance, in the recording operation using a light beam 1 modulated as shown in FIG. 2A, pits 11 and a groove 12 are, in general, obtained as shown in FIG. 2B.
However, in the above-described conventional recording apparatus, the same recording beam and the same focused spot size are used to record both the pits 11 and the groove 12. Therefore, in this apparatus, the only way to change the pit or groove configuration is to control the recording power. Thus, the recording performance of the conventional apparatus is limited to some degree. Furthermore, the conventional recording apparatus is disadvantageous in that only a single wavelength light beam is used for recording.